Spherical roller bearings have the property that they will accomodate a certain degree of shaft misalignment. The inner race is capable of turning to a certain degree relative to the outer race. This action is not possible in other forms of roller bearing.
Roller bearings require lubrication. In many forms of roller bearing however, during operation the lubrication deteriorates and becomes dissipated. For these reasons such bearings must be re-lubricated at regular intervals.
To reduce the requirement for re-lubrication, and to exclude foreign matter, bearings may be sealed in various ways.
In the case of standard sealed roller bearings, in some cases, seals were placed between the inner and the outer race, so that the rollers are entirely enclosed. Examples are shown in U.S. Pat. Nos. 4,575,265, and 3,773,397. In most cases however, seals were mounted in the bearing housing and sealed directly on the shaft.
The use of a sealed bearing housing causes certain difficulties in replacing the bearing.
In the typical bearing housing, the housing is in two parts. The bearing is received in a recess in the bearing base, and a bearing cap is then bolted over the top of the bearing holding it in place.
The shaft is secured in the bearing by a split, tapered sleeve with a lock nut threaded on the smaller end. The sleeve and nut are located within the bearing.
If it is required to replace the bearing, then it is necessary to remove the housing cap, disconnect the shaft and raise it to a sufficient height that the sleeve and nut can be loosened and the bearing can be slid along the shaft clear of the lower part of the housing.
This is inconvenient and causes costly down time of machinery.
Since most bearings are installed in pairs, two to a shaft, it is apparent that both bearing housings must be opened to achieve this.
In the case of double row spherical roller sealed bearings, this situation was unsatisfactory for other reasons. Since spherical roller bearings are often used where some degree of shaft misalignment must be expected, the shaft misalignment impaired the effectiveness of the seals. Since the seals bore directly on the shaft itself, any deflection of the shaft would impair the seal. In addition, the provision of such seals in the bearing housing caused some additional expense.
Bearing housings of a one piece construction are known. In these bearing housings, the bearings are held in a one piece housing by means of circlips or the like.
Bearing housings of this type have an advantage over the typical two part housing. In this type of housing, if it is desired to replace the bearing, then the housings are simply unbolted from the base structure, and the shaft and both bearings moved to a bench. The sleeve and nut are loosened since they are accessible from outside the housing, and the bearing and housing can be slid along the shaft. Replacement of the bearing can therefore take place without the necessity of removing the bearing from the housing. The replacement unit will typically be a complete bearing and housing.
However, this type of one piece bearing housing does not lend itself to the provision of seals mounted in the housing and riding on the shaft itself.
Some proposals have been made for locating seals between the inner and outer races of single row spherical roller bearings. Such bearings are distinct from double row spherical roller bearings. Single row spherical roller bearings are incapable of withstanding axial thrust loads. Examples of such single row spherical roller bearings are shown in U.S. Pat. Nos. 3,306,687, 3,748,003 and 3,361,497. The seals used in these patents would not be adaptable to double row spherical roller bearings.
U.S. Pat. No. 3,667,821 shows a double row spherical roller bearing with a seal on one side of the races but no seal on the other. This would not provide a "sealed for life" double row spherical roller bearing.
U.S. Pat. No. 4,671,682 also shows a double row spherical roller bearing with seals. In this case, the seals are located between what is described as an axle box enclosing the outer race, and a flange on the inner race.
Neither patent discloses a seal located between the inner and outer races of a double row spherical roller bearing.
For all of these reasons therefore it is considered desirable to provide a double row spherical roller bearing which is sealed for life, and in which the seals are unaffected by misalignment, and which is mounted in a one piece bearing housing open at both ends giving access to the split sleeve and nut by which the bearing is secured on the shaft.